| 摘要 |
PURPOSE:To improve remarkably the heat resistance of a composite material formed by joining the layer of a sintered body consisting of the binding phase of diamond and a ferrous metal to a sintered hard alloy base material when said material is used for a tool, etc. by removing the binding phase in the surface layer part of said body. CONSTITUTION:A composite sintered body in which a disc-shaped diamond sintered body 1 obtd. under ultrahigh pressure is joined to a sintered hard alloy base material 2 is manufactured. The sintered body 1 contains 90vol% diamond particles having, for example, 5mu average grain size and consists of the balance Co binding phase. The composite sintered body is placed in such a way that the surface of the body 1 contacts with the sponge of a plastic contg. diluted hydrochloric acid soln. and is rested for a required time while a prescribed DC voltage is impressed between the base material 2 and the electrode placed under the sponge. The binding metal Co phase in the certain region 1' from the surface of the body 1 is thus mostly electrolytically removed. The heat resistance of the composite sintered diamond as a tool is thus improved without deteriorating the strength thereof.
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